JPH0283208A - Production of graphite - Google Patents

Abstract

PURPOSE:To obtain block-like graphite excellent in locking characteristics, etc., by heat-treating specific high polymer films, superposing the resultant carbonaceous films and hot pressing the superposed carbonaceous films under specified conditions. CONSTITUTION:High polymer films 11 of 1-400mum thickness selected from aromatic polyimide, aromatic polyamide and polyoxadiazole, as necessary, are heat-treated at 450-2000 deg.C to provide carbonaceous films. plural sheets of the resultant films are then superposed and hot pressed while applying 20kg/cm<2> pressure at <=2800 deg.C and >=20kg/cm<2> pressure at >=2800 deg.C or intermittently applying <=50kg/cm<2> pressure at 800-2000 deg.C and 20-50kg/cm<2> pressure at >=2000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing block graphite used as X-ray optical elements, X-ray monochromators, neutron beam diffraction mirrors, neutron beam filters, and the like.

Conventional technology Graphite has outstanding heat resistance, chemical resistance, and high conductivity, so it occupies an important position as an industrial material.
Widely used as electrodes, heating elements, and structural materials. Among these, single crystal graphite has excellent spectroscopy and reflection characteristics for X-rays and neutron beams, and is therefore widely used as monochromators, filters, and spectroscopic crystals for X-rays and neutron beams.

To obtain such single crystal graphite, it is easy to use naturally occurring graphite, but high quality natural graphite is produced in very limited quantities and is difficult to handle in powder form. , or because it is in the form of a very small block, the applications for which it can be used are limited. Therefore, it was thought to produce artificial graphite that has properties equivalent to the above-mentioned natural single-crystal graphite. Common methods for producing artificial graphite can be mainly classified into the following two methods.

The first method involves precipitation from Fe, Ni/C melt, S
This is a method for producing graphite by decomposing carbides such as i, AI, etc., or by cooling a carbon melt under high temperature and high pressure. Graphite obtained by such a method is called quiche graphite and exhibits physical properties equivalent to natural graphite.

However, the above-mentioned method can only yield graphite in the form of minute flakes, and because the manufacturing process is complicated and the cost is high, it is hardly used industrially.

The second method is the high-temperature decomposition deposition of hydrocarbon gas in the gas phase and its hot processing. Graphite is produced through a process of re-annealing at 3400°C for a long time while applying pressure. . The graphite thus obtained is highly oriented bi. Graphai) ()-10PG)
Its properties are almost the same as natural graphite.

In this method, unlike the above-mentioned quiche graphite,
Although they can be manufactured in fairly large sizes, they have the drawbacks of complicated manufacturing processes, low yields, and very high costs.

In order to overcome the drawbacks of these two production methods and to produce graphite easily and at low cost, a method has been devised in which various organic substances or carbonaceous substances are heated at 3000° C. or higher to form graphite. However, by this method, it was not possible to obtain graphite having excellent properties equivalent to natural graphite or Quiche graphite. For example, the electric conductivity in the a-b plane direction, which is the most typical physical property of graphite, is 1 to 2.5 x 10' S for natural graphite and Quiche graphite.
/cm, whereas in the above method, generally 1
Only ~2X 103S/cm can be obtained. This indicates that graphitization does not proceed completely with the above method.

In the case of the above method, a carbonaceous material such as coke and a binder such as coal tar are usually used as starting materials, but the structure of the carbon produced by heating coke or charcoal to about 3000 degrees is There are a variety of types, ranging from those that are close to the structure of graphite (graphite) to those that are far from it. Among these carbon structures, carbon that relatively easily changes into a graphite-like structure by simple heat treatment is called graphitizable carbon, and carbon that does not change into a graphitizable carbon is called non-graphitizable carbon. The cause of such structural differences is closely related to the graphitization mechanism and depends on whether structural defects present in the carbon precursor are easily removed by heat treatment at a higher temperature. Therefore, the microstructure of the carbon precursor plays an important role in graphitizability.

In contrast to the above-mentioned method of using it as a starting material for coke, etc.,
Several studies have been conducted on methods for producing graphite films by heat-treating polymeric materials. This is an attempt to control the fine structure.

The above method heat-treats the polymer in vacuum or inert gas, converts it into a carbonaceous material through decomposition and polycondensation reaction,
This is a method of further graphitizing this carbonaceous material.

However, in the case of this method, graphite films with excellent properties cannot be obtained by using arbitrary polymers as starting materials; rather, it has been found that most polymeric materials cannot be used for this purpose. There is. For example, when heat treatment is attempted for the purpose of graphitization as described above,
Polymers used include phenol formaldehyde resin, polyparaphenylene, polyparaphenylene oxide,
Although there are polyvinyl chloride and the like, all of these polymers belong to materials that are difficult to graphitize and do not have a high graphitization rate.

The present inventors conducted various studies in order to solve the problems of the graphite production method using polymers as described above, and as a result of trying to graphitize a large number of polymers, they developed a film-like polyamide (PA). ), polyoxadiazole (POD), aromatic polyimide (PI), three types of polybenzobisthiazole (PBBT), polybenzoxazole (PBO), polybenzobisoxazole (PBBO), polythiazole (p'r) We have discovered that when heat-treated polymers such as, etc., at a specific temperature, they become graphitized more easily than conventionally known polymer materials. Based on these findings, the present inventors have filed patent applications, and these patent applications include JP-A-61-275114, JP-A-61-275115, and JP-A-61-27511.
It is disclosed in Publication No. 7, etc.

According to this method, the above-mentioned polymer is heated to 1800°C.
As mentioned above, graphite with a high graphitization rate can be easily produced in a short time by heating preferably at 2500° C. or higher.

X-ray diffraction parameters such as crystallite size in the C-axis direction,
Alternatively, the graphitization rate calculated therefrom is often used, and the electrical conductivity number is also often used. The lattice constant is calculated from the position of the (002) diffraction line of X-rays, and the closer it is to 6,708 A, which is the lattice constant of natural single crystal graphite, the more developed the graphite structure is. The crystallite size in the C-axis direction is calculated from the half-width of the (002) diffraction line, and the larger the crystallite value, the better the planar structure of graphite is developed. The size of graphite crystallite is 1000
Eight or more. The graphitization rate is calculated from the crystal plane spacing (d022) (Reference Nil Carbon Vol. 1, p. 129, 1
965-Les Carbons Vol, 1 p1
29.1965). Naturally, the graphitization rate of natural single crystal graphite is 100%. Electrical conductivity is indicated by the direction of the a-b plane of graphite, and the larger the conductivity, the closer it is to the graphite structure.In natural single crystal graphite, it is 1 to 2.5 x 10'S.
/cm0 Furthermore, one of the X-ray diffraction parameters for evaluating the graphite structure is the rocking property, which indicates how the a-b planes overlap. This is called a 1-diffraction intensity curve, and is a diffraction intensity curve obtained by rotating the crystal when a monochromatic, parallel X-ray flux is incident. 20 is fixed at the angle at which the (001) diffraction line appears, and θ is measured by rotating.

This directness is evaluated by the half-width of absorption, and the angle of one rotation (
0). The smaller the casing, the more clearly the a-b planes overlap.

Problems to be Solved by the Invention The method of producing graphite from a specific polymer film as described earlier is an excellent method as it is easy and inexpensive. As a result of further investigation, it became clear that there were several problems that needed to be improved, as listed below.

The first problem is that thick graphite or block-shaped graphite cannot be produced using this method. At first glance, the graphitization reaction seems to be unrelated to the thickness of the starting material film, but in reality, the graphitization reaction strongly depends on the thickness of the raw material. Although this has not been known at all in the past, the inventors have discovered the above-mentioned problem as a result of various experiments. For example, Table 1 shows the results of graphitizing four types of POD films with different thicknesses and measuring the lattice constant, graphitization rate, and electric conductivity in the a-b plane direction of the graphite.

Bottom Margin Table 1 From the above results, it can be seen that the degree of progress of the graphitization reaction clearly differs depending on the thickness of the POD film. For example, the graphitization rate varies from 99 to 87 inches depending on the thickness. This shows that although thin film-like graphite can be obtained using the same POD as a material, it is difficult to obtain thick block-like graphite.

Next, the second problem with the production method of the prior art is that simply heating the polymer raw material does not
This means that the locking characteristic, which is how neatly the surfaces in the surface axis direction overlap in the C-axis direction, is not improved.

Rocking properties are important properties when graphite crystals are used in X-ray optical elements, etc., and the above-mentioned rocking method using X-ray diffraction is used to measure how the a-b planes overlap. The locking properties when graphite crystals are used as optical crystals for X-rays, etc. vary depending on the application, but in general, a thin graphite film below 100 μm has a locking property of 0.4 μ below %1+mT.
For graphite blocks thicker than +, a thickness of 3°μ or less is required. On the other hand, in the case of I) 01) graphite shown in Table 1 above, the rocking properties are 6.7° (starting film thickness 5 μm, the same applies hereinafter),
10.5'(25ttm'), 12 (100μm)
, 17 (400 μm), and neither of them can satisfy the required locking characteristics. This indicates that in terms of locking properties, it is not possible to produce a radiation optical element with excellent locking properties simply by heating a polymer film to graphitize it. The reason for such poor rocking properties is considered to be that the thicker the film, the more difficult it is for the a-b plane to be oriented due to gas generation from inside the sample during heat treatment.

Therefore, the object of this invention is to solve the above-mentioned problems in the method of producing graphite by heat-treating a polymer film, and to solve the problem of producing graphite with excellent rocking properties and other properties as graphite. The purpose is to provide a method for manufacturing.

Means for Solving the Problems Among this invention for solving the above problems, the invention according to claim 1 provides a high-density polymer with a thickness of 1 to 400 μm selected from aromatic polyimide, aromatic polyamide, and polyoxadiazole. A carbonaceous film is produced by heat-treating a molecular film at 450 to 2000°C, and a plurality of the obtained carbonaceous films are stacked to give 20 to 9/cntLu at 2800°Cμ and 20kg/crA at 2800°C or higher. Heat and pressure bonding is performed while applying the above pressure.

The invention according to claim 2 provides carbonaceous film obtained by heat-treating a polymer film with a thickness of 1 to 400 μm selected from aromatic polyimide, aromatic polyamide, and polyoxadiazole to produce a carbonaceous film. A plurality of quality films are stacked one on top of the other, and the film is heat-pressed at 800°C or higher while applying a pressure below 50 kg/cm intermittently.

According to the invention described in claim 1, a carbonaceous film of good quality can be produced by heat-treating the specific polymer film, and by stacking a plurality of carbonaceous films and heat-pressing them, locking can be achieved. In addition to having excellent properties such as properties, it is possible to produce thick block-shaped graphite that cannot be obtained with a single layer film.

According to the second aspect of the invention, a carbonaceous film of good quality can be produced by heat-treating the specific polymer film, and when a plurality of carbonaceous films are stacked and heat-pressed, pressure is applied intermittently. In addition to this, it has very good locking properties and other properties.
It is possible to produce thick block-shaped graphite that cannot be obtained with a single layer film.

Examples First, in this invention, a film made of a polymer selected from aromatic polyimide, aromatic polyamide, and polyoxadiazole is used as a polymer film serving as a starting material. The material composition and formulation of the flum are appropriately selected and implemented depending on the use and manufacturing conditions.

The thickness of the polymer film used is 400 μm or less, preferably in the range of 1 to 400 μm. When the film thickness becomes thicker than 400 μm, only a carbon precursor with a disordered internal structure (i.e., non-graphitizable carbon) is produced due to the gas generated during the carbonization and graphitization process, and then heat compression bonding or hot pressing is performed. Even if the process is carried out, it is not possible to obtain high quality graphite. There is no particular restriction when the film thickness is thin, but 1 μm
If it becomes thinner than this, it is economically disadvantageous because it is necessary to manufacture a larger number of carbonaceous films in order to manufacture a graphite block of the same thickness.

The heat treatment temperature for manufacturing carbonaceous film is 450~
It is carried out in the range of 2000°C. Although heat treatment can be performed in a temperature range of 2000° C. or higher, hot pressing of heat treated material within the above temperature range gives better results to the quality of the graphite that is finally produced. This step is a preliminary heat treatment step before hot pressing, but at this stage it is better to heat-treat the polymer films separately without overlapping them, and in particular, it is better not to overlap them to a thickness of 400 μm or less. This is because if the polymer films are heat-treated in a stacked state, gas generation from the polymer films is suppressed, resulting in the same drawbacks as using thick films.

After manufacturing a carbonaceous film through the preliminary heat treatment process described above, multiple sheets of carbonaceous film are stacked and a hot press process, which is a full-scale heating and compression process, is performed to convert the carbonaceous to graphite. The process proceeds to produce block-shaped graphite. In this hot pressing process,
The method of pressure application and temperature control are important. That is, in this hot pressing step, it is necessary to press the carbonaceous film while removing wrinkles generated in the carbonaceous film during heat treatment. As a result of researching such processing conditions, 2800'C
In the following temperature range, the pressure must be 20 kg/cli1 or less, and if a pressure higher than the above pressure is applied in this temperature range, the carbonaceous film will crack. In addition,
It is more effective to prevent cracking if pressure is applied gradually rather than suddenly. In the temperature range above 2800℃, 20 kg to achieve perfect adhesion
/ A pressure higher than CIA is required, and crimping cannot be performed sufficiently at a pressure lower than CIA.

By going through the manufacturing process as described above, it is possible to manufacture graphite that has a thick block shape and has significantly improved rocking properties. For example, the POD film (thickness 4, 25, 10
0,450 μm) at 100° C. to produce a carbonaceous film, ten films of each thickness are stacked one on top of the other and subjected to a hot pressing process. The true breath process is a temperature raising process, and up to 2800℃ the temperature is 4 kg/c.
Applying a pressure of 2,800'C, 20
Applying a pressure of kg/cl and processing at 3000℃ for a certain period of time to produce block-shaped graphite.
When graphite was actually manufactured under the above processing conditions, its rocking properties were 1.0° (4 μm),
1.2° (25 μm), 165° (100 μm), 1.
8° (450 μm), and a significant improvement in rocking properties was observed.

Next, a manufacturing method that is partially different from the above method, and which similarly has excellent rocking properties and can manufacture thick block-shaped graphite, will be described.

The material of the polymer film and the heat treatment process for manufacturing the carbonaceous film can be carried out in the same manner as the manufacturing process of the above-mentioned embodiments, so a detailed explanation will be omitted. In the manufacturing method of this example, in the hot pressing step, 8
It is characterized by applying pressure intermittently in a temperature range of 00°C or higher. As mentioned above, in the hot pressing process of carbonaceous films, it is important to effectively eliminate wrinkles and distortions caused by heat treatment, and in this respect, continuous application of pressure is extremely important. It is valid.

When applying continuous pressure, it is more effective to keep the maximum pressure relatively small in the low temperature range of the heat treatment process, and increase the maximum pressure in the high temperature range. It's thick. The maximum pressure applied is
Below 2000℃, it is most desirable to be under 20kg/cf IU, but 50kg/ct? It is effective if it is below rμ. 20 kg/cn above 2000℃
It is desirable to be on t Id, but 50 to 9/ct?
Pressure above + is not necessary.

-Example- Next, a specific example in which graphite was manufactured by the manufacturing method of the present invention will be described.

In each example, in order to evaluate the degree of graphitization, the above-mentioned lattice constant, graphitization rate, electrical conductivity, and rocking properties were measured, and the measurement conditions for these physical properties were as follows.

(1) Lattice constant (Co) The X-ray diffraction line of the sample was measured using a CuKa beam using a 1) W-1051 X-ray diffractometer manufactured by Philips. From the (002) diffraction line appearing around 2θ=26 to 27°, the graph formula nλ=2dsi
Calculated using nθ (where 2d=Co). here,
0=2, λ is the wavelength of the X-ray.

(2) Graphitization rate (H) The graphitization rate was calculated from the interplanar spacing (d) using the following formula.

d002=3.354 g+3.44 (1-g)
Here, 1 g indicates the degree of graphitization, g=1 represents complete graphite, and g=o represents amorphous carbon.

(3) Electrical conductivity (S/cm) Measured by attaching a 4-terminal electrode to the sample using silver paste and gold wire, flowing a constant current from the outer electrode, and detecting the voltage drop at the inner electrode. . The electrical conductivity was calculated from the results of measuring the width, length, and thickness of the sample using a microscope.

(4) Rocking properties (o) Using a Rotaflex RU-200B model X-ray diffractometer manufactured by Rigaku Denki Co., Ltd., the rocking properties at the peak position of the graph eye l-(002) line were measured. The half width of the obtained absorption curve was taken as the rocking characteristic.

Example Am A 10 μm thick POD, PA, and PI polymer film was sandwiched between graphite plates and heated to 1000°C at a heating rate of 20°C per minute in a nitrogen atmosphere. Heat treatment was performed by holding for 1 hour to obtain a carbonaceous film.

Twenty carbon films made of each material were stacked one on top of the other, and a hot pressing process was performed using an ultra-high temperature hot press manufactured by Chugai Roko Kogyo Co., Ltd. to obtain a graphite block. The processing conditions of the hot press step were to raise the temperature at a rate of 10°C per minute, gradually apply pressure in the temperature range of 1000 to 2800°C, and finally increase the pressure to 20 kg/cnt. In the temperature range above 2800℃, the pressure should be reduced to 40 kg.
/C% and pressed at 3000°C for 1 hour. The physical properties of the graphite block obtained in this way are
Shown in the table.

μ bottom margin Part 2 table Polymer fiber lattice constant graphitization rate Lum material C.

(A) (H) Electrical locking conductivity properties (S/cm) (') POD 0.9 PA 6.708 0.8 PI 6.708 0.65 According to the above results, the obtained graphite The locking properties of the block range from 0.9 to 0.65°,
It has been demonstrated that block-shaped graphite having excellent rocking properties can be produced by the production method according to the invention set forth in claim 1.

Example B- PI films having thicknesses of 2, 10, 25, 50, 100, and 200 μm were heat-treated at 1000° C. to produce carbonaceous films. Two to 20 sheets of each carbonaceous film were piled up, and a hot pressing process was performed under the same processing conditions as in Example 1 with various total thicknesses.

The locking properties of the obtained Gra7ite block were evaluated as
Shown in the table.

μ Lower Margin Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Third Table 0. 50 0.65 0.62 0.67 0.65 0.67 0.72 0.85 0.82 0.96 1.54 1.29 2.21 2.01 From the above results, the starting material It can be seen that the thicker the molecular film is, the worse the locking properties are, and in order to suppress the rocking properties to within 1 μm, it is necessary to use a polymer film with a thickness of 400 μm or less. Note that as the number of stacked polymer films increases, the locking properties tend to deteriorate, but the degree of this is not so significant.

Example C - Polymer films of POD, PA, and PI with a thickness of 25 μm were sandwiched between graphite plates and heated to 1000°C at a heating rate of 20°C per minute in a nitrogen atmosphere, and then heated to 1000°C. A heat treatment was performed by holding the mixture for 1 hour to obtain a carbonaceous film.

20 carbonaceous films made of each material were stacked one on top of the other and subjected to a hot pressing process using an ultra-high temperature hot press manufactured by Chugai Roko Kogyo Co., Ltd. to obtain a Gra7ite block. The processing conditions of the hot press step are to raise the temperature at a rate of 10°C per minute, in a temperature range of 1000 to 2800°C,
θ~20kl? /0% pressure was applied intermittently 12 times. The method of applying pressure is to gradually increase the pressure from a state of 0 pressure to a maximum pressure of 20 kgZc- in about 2 minutes,
After maintaining this maximum pressure for 2 minutes, the pressure was returned to zero in about 1 minute.

After maintaining the pressure at 0 for 3 minutes, the same pressurizing operation as above was repeated. Next, when the temperature was raised to a temperature range of 2800° C. or higher, the maximum pressure was set to 50 kg/cnt, and the same intermittent pressure application as described above was performed.

After raising the temperature to a maximum temperature of 3000°C, it was pressed at 3000°C for 1 hour. Table 4 shows the physical properties of the graphite block thus obtained.

Table 4 Polymer Phi Lattice Constant Graphitization Rate Electric Rocking Lum Material Co Conductivity Characteristics (A) (
%) (S/cm) (0) OD 6.708 A 6.708 I 6.708 0.62 0.60 0.51 From the results above the bottom margin, the rocking properties of the obtained graphite flock are 0 .62 to 0.51', and it has been demonstrated that block-shaped graphite having excellent rocking properties can be produced by the production method according to the invention set forth in claim 2. Furthermore, when comparing the results of Example C with the results of Example A, the locking properties are higher, indicating that applying pressure intermittently during the hot pressing process is more effective in improving the locking properties. I was able to prove it.

Effects of the Invention Of the method for producing graphite according to the present invention described above, according to the invention described in claim 1, after a specific polymer film is heat-treated to produce a carbonaceous film, a plurality of carbonaceous films are By stacking films and hot-pressing, that is, heat-pressing them, it is possible to produce graphite that has excellent properties such as rocking properties and has a thick block shape. As in the conventional method, 1
If only a single sheet of polymer film is heat-treated, the film becomes thicker and the properties of the graphite deteriorate.However, with the manufacturing method of this invention, a thin polymer film is pre-heat-treated to produce high-quality carbon. After obtaining a carbonaceous film, this carbonaceous film is thermocompressed in a hot press process to obtain block-shaped graphite with a predetermined thickness, so even if the thickness of the graphite to be manufactured becomes thick, the properties will not deteriorate. Although it is thick block-shaped graphite, it is possible to obtain graphite that has the same excellent properties as graphite made of a thin polymer film alone.

Therefore, it is possible to easily produce graphite with excellent properties, which has been difficult to produce in the past. ! It becomes possible to obtain block-shaped graphite with significantly improved rocking properties, etc., compared to other methods. The thick block-shaped graphite produced by the production method of the present invention and having excellent locking properties can be widely used in X-ray and neutron beam monochromators, filters, and the like.

Further, according to the invention described in claim 2, after manufacturing a carbonaceous film in the same manner as in the invention described in claim 1, the invention according to claim 1 is produced by applying pressure intermittently in a hot pressing process. In addition to the above-mentioned effects, it is possible to further improve locking characteristics and the like.

Claims (2)

[Claims] (1) A polymer film with a thickness of 1 to 400 μm selected from aromatic polyimide, aromatic polyamide, and polyoxadiazole is heat-treated at 450 to 2000°C to produce a carbonaceous film, and the obtained carbon 20kg/cm in the temperature range below 2800℃ by stacking multiple sheets of quality film
20kg/c in the temperature range below ^2 and above 2800℃
A method for producing graphite in which heat and pressure bonding is performed while applying a pressure of m^2 or more. (2) producing a carbonaceous film by heat-treating a polymer film with a thickness of 1 to 400 μm selected from aromatic polyimide, aromatic polyamide, and polyoxadiazole;
The resulting carbonaceous films were stacked together to produce a weight of 50 kg/c.
A method for producing graphite in which heat and pressure bonding is carried out at a temperature of 800°C or higher while continuously applying a pressure of m^2 or less.